Synthesis of ethyl t-butyl ether from t-butanol using b-zeolite and multimetal-modified b-zeolite catalysts

Abstract: A process for preparing ethyl t-butyl ether in one step which comprises reacting tertiary butanol and ethanol in the presence of a catalyst selected from β-zeolite and β-zeolite modified with multimetals selected from the group consisting of Groups IB, VB, VIB, VIIB or VIII of the Periodic Table at a temperature of 20°C to 250°C and 0.1 to 7.0 MPa. The product comprises a two-phase mix of an ETBE-isobutylene and, optionally, diisobutylene product-rich phase and a heavier aqueous ethanol-rich phase.

Description: The present invention relates to an improved process for preparing ethyl tertiary butyl ether (ETBE) in one step by the reaction of tertiary butanol and ethanol in the presence of a catalyst comprising a β-zeolite alone or modified with one or more metals selected from the group consisting of Groups IB, VB, VIB, VIIB and VIII of the Periodic Table as defined in the Condensed Chemical Dictionary, page 789. Metals which work well include transition metals found in Row 1 of Groups IB, VIB, VIIB, and VIII, particularly iron, copper, chromium, manganese, and nickel. The invention is especially advantageous in that the multimetal-modified zeolites exhibit both high activity during ethyl t-butyl ether synthesis from ethanol plus t-butanol and, additionally, allow for the cosynthesis of isobutylene and diisobutylene. Generally, it is known that asymmetrical C 4 -C 7 alkyl tertiary alkyl ethers are particularly useful as octane improvers for liquid fuels, especially gasoline. Methyl tertiary butyl ether (MTBE), ethyl t-butyl ether (ETBE), isopropyl t-butyl ether (IPTBE) and tertiary amyl methyl ether (TAME) are known to exhibit high octane properties. Much attention has been focused on production of these ethers due to the rapidly increasing demand for lead-free octane boosters for gasoline. It is known in the art to produce ETBE or MTBE by reacting isobutylene with either ethanol or methanol, resulting in the formation of ETBE of MTBE, respectively. The reaction normally is conducted in liquid phase with relatively mild conditions. The isobutylene can be obtained from various sources, such as naphtha cracking and catalytic cracking. The resulting reaction product stream contains the desired MTBE or ETBE, as well as unreacted isobutene and other C 4 hydrocarbons and methanol or ethanol. Ethyl tertiary-butyl ether has long been recognized as a suitable blending cosolvent for hydrous ethanol in gasoline stocks. ETBE can be blended into a fuel gasoline at about a 10 to 20 volume percent level, usually nearer 9 to 12%, in which the fuel comprises about 70 to 84% gasoline and 5 to 20% of 95% ethanol, i.e. grain alcohol. ETBE solubilizes grain alcohol in gasoline in all proportions thereby allowing a wide latitude in the precise amount of ethanol which can be blended with gasoline. There has previously been some interest in the use of ethyl-tertiary-butyl ether (ETBE) as a lead free octane booster for gasoline. Note, for example, the following publications: Iburra et al., "Getting the Lead Out With Ethyl t-Butyl Ether," CHEM TECH, Feb. 1988, pp. 120-122 and Verbanic, "ETBE: Ethanol's Motor Fuel Hope?" CHEMICAL BUSINESS, Oct. 1988, at pp. 38-39 and the paper presented at the DeWitt Petrochemical Review, Houston, Texas, March 28-30, 1989, by Neerlich et al., entitled "Huels/UOP Technology for ETBE/MTBE Production." Recently, there has been increased interest in ETBE due to efforts in Washington, D.C., to extend tax credits for corn-based ethanol used to produce ETBE. A number of U.S. patents and European patents and applications of Texaco Chemical Co. disclose methods of making alkyl tertiary alkyl ethers, including ETBE, in one step. In US-A-4,822,921 there is described a method for preparing alkyl tertiary alkyl ethers, including ETBE, which comprises reacting a C 1 -C 6 primary alcohol with a C 4 -C 10 tertiary alcohol over a catalyst comprising an inert support impregnated with phosphoric acid. US-A-4,827,048 describes a method for preparing alkyl tertiary alkyl ethers from the same reactants using a heteropoly acid on an inert support. US-A-5,099,072 discloses a method for preparing alkyl tertiary alkyl ethers, including ETBE, over an acidic montmorillonite clay catalyst which possesses very specific physical parameters. US-A-5,081,318 discloses a method for preparing alkyl tertiary alkyl ethers by reacting a C 1 -C 6 primary alcohol with a C 4 -C 10 tertiary alcohol over a catalyst comprising a fluorosulfonic acid-modified zeolite. US-A-5,059,725 discloses a method for preparing alkyl tertiary alkyl ether, including ethyl tertiary butyl ether, from C 1 -C 6 primary alcohols and C 4 -C 10 tertiary alcohols over a catalyst comprising ammonium sulfate or sulfuric acid on a Group IV oxide. US-A-5,157,162 discloses a fluorosulfonic acid-modified clay catalyst for the production of, ETBE, inter alia, from C 1 -C 6 primary alcohols and C 4 -C 10 tertiary alcohols. In US-A-5,162,592 there is described a method for producing alkyl tertiary alkyl ethers from C 1 -C 6 primary alcohols and C 4 -C 10 tertiary alcohols using a multimetal-modified catalyst. A hydrogen fluoride-modified montmorillonite clay catalyst is employed in US-A-5,157,161 to produce alkyl tertiary alkyl ethers, including ETBE. In US-A-5,183,947 fluorophosphoric acid-modified clays are employed as catalysts in a method to produce alkyl tertiary alkyl ethers. In EP-A-0594283 there is disclosed the use of a super acid alumina or a faujasite-type zeolite to produce alkyl tertiary alkyl ethers. EP-A-059168 discloses the use of a haloacid-modified montmorillonite clay catalyst to convert C 1 -C 6 primary alcohols and C 4 -C 10 tertiary alcohols to alkyl tertiary alkyl ethers. EP-A-0595567 describes the synthesis of MTBE using β-zeolite or metal modified β-zeolite. No specific description is given of the use of such a process in the preparation of ETBE. Other references in the art which disclose ETBE as a product usually require two stages rather than one and use isobutylene as a reactant. For example, in US-A-4,334,890, a mixed C 4 stream containing isobutylene is reacted with aqueous ethanol to form a mixture of ethyl tertiary butyl ether (ETBE) and tertiary butyl alcohol (TBA). US-A-5,015,783 describes a process for producing ethers, including ETBE which comprises passing a feed stream to an etherification zone, passing the etherification zone effluent stream to a distillation column and further involves cooling the overhead stream, refluxing and recycling. A process for the production of ETBE and/or MTBE is disclosed in US-A-2,480,940. U.S. Patents which discuss the production of ETBE as well as MTBE include: US-A-5,070,016 US-A-4,440,063 US-A-4,962,239 US-A-4,015,783 These patents all use isobutylene as the coreactant rather than t-butanol. The use of zeolites for certain reactions is known in the art. β-zeolite was first synthesized at Mobil R and D labs and exhibited improved thermal and acid stability over previously synthesized zeolites. Patents in the art which employ β-zeolite relate mainly to dewaxing, and cracking of hydrocarbon feedstock. An article titled "β-Zeolite as Catalyst or Catalyst Additive for the Production of Olefins During Cracking or Gas Oil," was written by L. Bonetto et al., 9th International Zeolite Conference, July 1992, FP 22. The authors note that with the greater demand for oxygenated compounds there is indication there might be increased demands for catalysts and conditions which maximize C 3 , C 4 and C 5 olefins. They suggest that β-zeolite could be used alone or combined with Y-zeolite as a suitable zeolite component. Various catalysts were studied with respect to minimization of diffusional requirements and zeolite stability. Another European Application to Mobil, EP-A-0 094 82, discloses simultaneous catalytic hydrocracking and hydrodewaxing of hydrocarbon oils with β-zeolite. US-A-4,518,485, to Mobil, discloses a process for dewaxing a hydrocarbon feedstock containing paraffins selected from the group of normal paraffins and slightly branched paraffins and sulfur and nitrogen compounds where, after conventionally hydrotreating the feedstock to remove sulfur and nitrogen, the hydrotreated feedstock is dewaxed by contacting the feedstock with a catalyst comprising β-zeolite having a silica/alumina ratio of at least 30:1. In US-A-4,740,292 there is disclosed a catalytic cracking process which comprises cracking a hydrocarbon feed in the absence of added hydrogen with a cracking catalyst comprising a β-zeolite component and a faujasite component comprising at least one crystalline aluminosilicate of the faujasite structure, the weight ratio of the faujasite component to the β-zeolite component being from 1:25 to 20:1. Large pore β-zeolite has been employed in the synthesis of industrially important para-cymene by toluene isopropylation. See "Toluene Isopropylation over β-Zeolite and Metallosilicates of MFI Structure," P.A. Parikh et al., Applied Catalysis , A , 1992, 90 , p. 1. From available art, there do not appear to be methods available for adapting a catalyst to produce ethyl tertiary butyl ether in high yields in one step by reacting ethanol instead of methanol with tertiary butanol. It would be a valuable advance in the art if a method were available for the synthesis of ethyl tertiary butyl ether employing one step technology and a catalyst exhibiting extended life which accommodates the use of various grades of ethanol, i.e. denatured, grain and pure with tertiary butanol, rather than isobutylene. The cosynthesis of isobutylene and diisobutylene using the crude feedstock reactants would make such a process even more attractive. In accordance with certain of its aspects, the novel method of this invention for preparing ethyl tert-butyl ether (ETBE) from tertiary butyl alcohol and ethanol in one-step comprises reacting tertiary butyl alcohol and ethanol in the presence of a catalyst comprising β-zeolite or multimetal-modified β-zeolite at an elevated temperature and moderate pressure. Preparation of the product of this invention may be carried out typically by reacting tertiary butyl alcohol and ethanol in the presence of an etherification catalyst. The etherification is carried out in one-step and the catalyst comprises a β-zeolite or a β-zeolite modified with one or more metals selected from the group consisting of Group IB, VB, VIB, VIIB and VIII of the Periodic Table. The reaction can be represented by the following: Generally the ethanol and t-butanol coreactants may be mixed in any proportion in order to generate the desired ethyl t-butyl ether (ETBE), but preferably the molar ratio of ethanol to t-butanol (tBA) in the feed mixture should be between 10:1 and 1:10, if the yield of desired ETBE is to be maximized. In order to achieve maximum selectivity to ETBE, and optimum conversion per pass, an excess of ethanol in the liquid feed is desirable. The most preferred ethanol-to-tertiary butanol molar ratio is from 1:1 to 5:1. In certain circumstances, the tBA conversion is high enough (e.g. 70% or greater), such that the crude product mix phase separates into an isobutylene-ETBE product-rich phase and a heavier aqueous ethanol phase. Optionally the ETBE-isobutylene phase will also contain diisobutylene. Preferably such a product phase separation would be achieved at as low an etherification temperature as possible, but it is particularly observed in the range 140°-200°C. The synthesis of Eq. 1 can also be conducted where the t-butanol and ethanol reactants are mixed with certain other components including water, ketones such as acetone (Me 2 Co) and methyl ethyl ketone (MEK), peroxides and hydroperoxides such as di-t-butyl peroxide (DTBP) and allyl t-butyl peroxide (ATBP), and t-butyl hydroperoxide (TBHP), as well as esters such as t-butyl formate (TBF). Typically each of said classes of components makes up less than 10% of the total feed mixture. It has been discovered in the instant invention that the β-zeolites and the multimetal-modified β-zeolite catalysts herein disclosed function to exhibit concurrent quantitative decomposition of peroxide in the alcohol feedstock in addition to converting tertiary butanol plus ethanol to ETBE. This constitutes an important advantage in a commercial setting. In the modified catalyst of the instant invention good results were realized using the β-zeolites as catalysts for the reaction. A review of β-zeolites and metal modified 8-zeolites is provided in EP-A-0595567 of Texaco Chemical Company. Particularly effective in the subject synthesis of ETBE are the β-zeolites modified with multiple metals. Illustrative of suitable β-zeolites for the practice of this invention include Valfor C806β, Valfor CP815β and Valfor C861. Valfor® is the registered trademark of the PQ Corporation. Valfor® C806β zeolite is zeolite beta powder in template cation form. It is a high silica shape selective zeolite which contains the organic template used in the crystallization step, having been isolated after filtration and washing of the synthesis product. C806β has a SiO 2 /Al 2 O 3 molar ratio of 23-26; the crystal size is 0.1-0.7 µm; the surface area after calcination is about 700-750 m 2 /g; the cyclohexane adsorption capacity after calcination is 19-24g/100g; Na 2 O content is about 0.01-1.0% by weight anhydrous; and, the organic content is about 11-13% by weight, on a water-free basis. Valfor® C815β zeolite is a calcined zeolite beta powder in hydrogen, sodium form. It is similar to C806β except the product has been calcined to decompose the organic template. C815β is a high silica, shape selective aluminosilicate with a large pore diameter. C815β also has a SiO 2 /Al 2 O 3 molar ratio of about 23-26; the crystal size, surface area, cyclohexane adsorption capacity and Na 2 O are all within the same ranges as given for C806β, Valfor® C861β is an extrudate made of 80% C815β powder and 20% alumina powder. The metals useful for modifying the zeolite in the instant invention comprise those from Group IB, VB, VIB, VIIB and VIII of the Periodic Table, including said transition metals. Preferred metals are those found in Row 1 of Groups IB, VIB and VIII of the Periodic Table and include copper, chromium, manganese, iron and nickel. Especially good results were observed using combinations of iron, manganese and chromium or combinations of nickel, copper and chromium, on VALFOR® Zeolite 861β. Said zeolites are preferably impregnated with said specified metals as their salts, particularly their metal nitrate or chloride salts, in an aqueous, alcoholic, or ketonic media over a period of 1-24 hours, then the solids are filtered off, dried at elevated temperature, e.g. 120°C, for a period of time and calcined at 300-800°C for a further period, e.g. 315°C for 2 hours, followed by 540°C for another 2 hours. Example 1 demonstrates the preparation of the multimetal-modified catalysts. Salts of iron, chromium and manganese, such as their chlorides or nitrates, in anhydrous or hydrated forms were dissolved in water, alcohol, or acetone and the β-zeolites were added, most often, in the form of extrudates. The catalysts were then calcined by heating to 300° to 800°C and optionally reduced in a stream of hydrogen at 200°C. The amount of the various metals deposited on the zeolite can vary. The amount of each individual metal, i.e., iron, chromium, copper, manganese, and nickel, can vary from 0.01 to 10.0%. Where iron, chromium and manganese are deposited on 861β the preferred weight percent is from 0.1% to 5.0%. Said catalysts may be in the form of powders, pellets, granules, spheres, shapes and extrudates. The examples described herein demonstrate the advantages of using extrudates. The reaction may be carried out in either a stirred slurry reactor or in a fixed bed continuous flow reactor. The catalyst concentration should be sufficient to provide the desired catalytic effect. Said catalysts may be formed in the presence of a binder, such as Group III or Group IV oxide, including alumina or silica. Said binders may comprise 10% to 90% of the formed catalyst. Etherification can generally be conducted at temperatures from 140°C to 200°C. Good results are observed throughout this temperature range. However, it can be noted that the best conversion figures for DTBP and tert-butanol are observed when the temperature is around 140°C or higher. The total operating pressure may be from 0.1 to 7.0 MPa (0 to 1000 psig), or higher. The preferred pressure range is 0.4 to 3.4 MPa (50 to 500 psig). Typically, ETBE is generated continuously in up to ca. 50 wt% concentration or greater in the crude liquid product at total liquid hourly space velocities (LHSV) of up to 6 or higher and relatively mild conditions, where: LHSV = Volume Of Total Liquid Feed Run Through The Reactor Per Hour Volume of Catalyst In Reactor Conversions of t-butanol (tBA, wt%) are estimated in the following examples using the equation: (Mole% of tBA in Feed - Mole% of tBA in Product) Mole% of tBA in Feed x 100 The examples which follow illustrate the one-step synthesis of ETBE from tBA and EtOH (Eq. 1) using β-zeolites or multimetal-modified β-zeolites particularly in the form of extrudates. In particular, the accompanying examples illustrate: 1) The cosynthesis of ETBE, isobutylene (C 4 H 8 ) and diisobutylene (C 8 H 16 ) in Example 2 from t-butanol (tBA) plus ethanol via etherification, dehydration and dimerization reactions using an iron, chromium, manganese-modified β-zeolite prepared by the method of Example 1. Here tBA conversion levels are typically 66% at 120°C and product phase separation is realized at temperatures of 160°C or above. 2) In Example 3, the cosynthesis of ETBE, isobutylene and diisobutylene from tBA/EtOH is illustrated using β-zeolite where tBA conversions are 71% at 120°C and 97% at 180°C. Again product phase separation into an ETBE, isobutylene and, optional diisobutylene-rich phase and a heavier aqueous ethanol phase is realized at 140°C. 3) Experiment 4 illustrates the cosynthesis of ETBE and isobutylene via ethanol/t-butanol etherification using a crude feedstock also containing sizeable quantities of water, isopropanol (2-PrOH), acetone Me 2 CO and methyl ethyl ketone (MEK). An extended catalyst life with this feed has been demonstrated. The examples are only intended as a means of illustration and it is understood the invention is not meant to be limited thereby. EXAMPLE 1 This example illustrates the preparation of a multimetal-modified β-zeolite. To 102g of β-zeolite (Valfor C861β, 80% β-zeolite, 20% alumina) in 1.6mm (1/16") diameter extruded form was added a solution of ferric chloride hydrate (1.04g), chromium(III) nitrate, hydrate (1.64g) and manganese(II) nitrate hydrate (1.10g) in 92 cc of distilled water. Impregnation of the β-zeolite was allowed to occur over 1-2 hours, then the solids were filtered off, dried at 120°C overnight, and calcined at 315°C for 2 hours, followed by 540°C for another 2 hours. The recovered green solid extrudates showed the presence of: %Fe = 0.27 %Cr = 0.19 %Mn = 0.08 Acidity = 0.35 meq/g EXAMPLE 2 This example illustrates the production of ethyl t-butyl ether from t-butanol and ethanol using the Fe, Cr, Mn-impregnated β-zeolite of Example 1. Synthesis was conducted in a tubular reactor (12.7mm internal diameter, 305mm long) constructed of 316 stainless steel, operated upflow and mounted in a furnace, controllable to ±1.0°C and fitted with pumps allowing flow control to <±1 cc/hr. The reactor was also fitted with a pressure regulating device and equipment for monitoring temperature, pressure and flow rate. The reactor was charged at the beginning of the experiment with 25 cc of a Fe, Cr, Mn-treated β-zeolite, prepared by the procedure of Example 1, as 1.6mm (1/16") diameter extrudates. A glass wall screen was placed at the top and bottom of the reactor to ensure the catalyst would remain in the middle portion. The catalyst bed was treated with an ethanol/t-butanol (1.1:1 molar mix) upflow, at a rate of 50 cc/hr, while the reactor was held at 120°C, with a total pressure of 2.1 MPa (300 psi). Samples of crude product effluent were collected periodically on stream, in 316 ss bombs and analyzed by glc. Typical analyses data for samples taken under these conditions are summarized in Table 1. Concentrations of ETBE, isobutylene, diisobutylene (C 8 H 16 ), diethyl ether (DEE), ethanol, and t-butanol in the reaction effluent were also measured at a series of higher temperatures (140-160°C). These data are also included in Table 1. For Sample #1, at 120°C: tBA Conversion = 66% ETBE Selectivity = 58% Isobutylene Selectivity = 28% Diisobutylene Selectivity = 12% For Sample #5, at 160°C: tBA Conversion = 89% EXAMPLE 3 Using the equipment and following the procedures of Example 2, a β-zeolite catalyst (C861β from PQ Corp., 80% Beta, 20% alumina) was treated with 1.1:1 molar mix of ethanol and t-butanol at a series of operating temperatures from 120° to 180°C. Concentrations of ETBE, isobutylene, diisobutylene, diethyl ether, ethanol and t-butanol in the product effluents, under the specified conditions, as determined by glc, are summarized in the accompanying Table 2. Of particular note: For Sample #2, at 120°C tBA Conversion = 71% ETBE Selectivity = 46% Isobutylene Selectivity = 24% Diisobutylene Selectivity = 26% For Sample #8, at 180°C: tBA Conversion = 97% (EXPERIMENT 4) Using the equipment and following the procedures of Example 2, a sample of β-zeolite catalyst (80% Beta, 20% alumina) was treated with a crude 1.5:1 molar mix of ethanol and t-butanol feedstock that also contains significant quantities of water, isopropanol (2-PrOH), acetone and methyl ethyl ketone. Etherification was conducted at 120°C, using a LHSV of 2. Concentrations of each of these components, plus isobutylene, diisobutylene, diethyl ether and ETBE, in the product effluents was determined by glc. Typical data are given in the accompanying Table 3. Over the period of the experiment (>1000 hours), there was essentially no change in catalyst activity as measured by the level of t-butanol conversion. Typical calculated conversion data are as follows: Sample 1 3 8 Time on Stream (Days): 1 13 43 t-Butanol Conv. 62 62 61

Claims: A process for synthesizing ethyl tertiary-butyl ether which comprises reacting t-butanol with ethanol in the presence of a catalyst selected from β-zeolite or a β-zeolite modified with one or more metals selected from Groups IB, VB, VIB, VIIB and VIII of the Periodic Table and continuously contacting said ethanol and t-butanol in a molar amount of from 10:1 to 1:10 over said zeolite catalyst at a pressure of 0.1 MPa to 7.0 MPa to obtain ethyl tert-butyl ether product, characterised in that the operating temperature is in the range of 140°C to 200°C and the product comprises a two-phase mix of an ETBE-isobutylene, and, optionally, diisobutylene product-rich phase and a heavier aqueous ethanol-rich phase. A process as claimed in Claim 1 wherein the β-zeolite is modified with one or more metals selected from Groups IB, VB, VIB, VIIB and VIII of the Periodic Table.

Inventors: DAI PEI-SHING EUGENE, KNIFTON JOHN FREDERICK, DAI, PEI-SHING EUGENE, KNIFTON, JOHN FREDERICK
Applicants: TEXACO CHEM INC, TEXACO CHEMICAL INC.
Application year: 1994
Main classification: C07C43
IPC codes: C07C41, B01J29, C07B61, C07C43